1. FIELD OF THE INVENTION
This invention relates to systems for measuring particular quantities of compositions in a fluid. In particular, this invention pertains to systems for measuring partial oxygen pressure in fluid samples. More in particular, this invention relates to a portable system for quantitating the amount of dissolved oxygen in solution within a fluid sample. More in particular, this invention relates to a measuring system utilizing an open type electrode sensing device. Still further, this invention relates to a system for analyzing fluid samples in a closed volume chamber by passage of current through a predetermined circuit within an open type electrode sensor. Additionally, this invention relates to a measuring system which simultaneously heats the fluid sample to a predetermined temperature and measures the current being passed through an electrode sensor containing the fluid sample in order to provide a readout of the amount of predetermined constituents contained in the fluid sample. Still further, the invention pertains to a measuring system where a fluid containing sensor is inserted into a hand held housing and actuation of the measuring system is dictated by application of the closing of lid of the housing to provide heating and current flow to the electrode sensor. Additionally, this invention relates to a measuring system which utilizes a wrap around type of heating assembly to maximize the heat transferred to a fluid sample while minimizing the temperature gradients created in the fluid sample.
2. PRIOR ART
Measuring systems for quantitating the amount of dissolved oxygen in fluid samples are known in the art. In some prior systems, such as those commonly referred to as a Clark electrode, a base reference and a cathode are placed behind a permeable membrane defining a chamber having an electrolyte contained therein. The gas to be measured then diffuses through the membrane and such is electrically and physically isolated in the solution, Appropriate currents are passed through the system and readings of the quantity of gas are measured. However, in such like prior systems, the electrolyte may be found to dry out. The electrolyte must then be replaced which is a difficult and time consuming procedure. Additionally, in such prior systems the membrane has been found to rupture and replacement of such has been found to additionally add to the costs of measuring fluid samples with such prior art systems.
Additionally, in prior systems of the permeable membrane type, consumption of the oxygen by the electrode may form a diffusion gradient in the liquid sample external to the membrane. Such diffusion gradients lead to erroneous readings of the percentage of the constituent being measured in the fluid sample.
In some such prior systems the temperature of the fluid sample has not been easily controlled within sufficiently restrictive tolerance ranges so as to provide constant reproducable readings of fluid sample measurements.
In other prior systems where fluid sample temperatures were maintained constant, circulating pumps were necessary to restrict temperature excursions. This increased the hardware cost and eliminated the possibility of producing a portable measurement system.
In other prior systems, where open electrodes were utilized, protein poisoning due to relatively long electrode/fluid sample exposure time, was found to be a major disadvantage. The resulting protein poisoning reduced the accuracy and associated repeatability of the fluid sample measurements.